Research Interests:
My research interests focus on
global and regional atmospheric impacts of anthropogenic pollutants
and boreal wildfires and the interactions of snow, ice, air and
light.
The global budget and cycling of nitrogen oxides plays a dominant role
in the budget of tropospheric ozone and, through ozone, is a
determinant of tropospheric oxidative strength. However, measurements
of nitrogen oxides in remote regions (most of the earth) are extremely
limited. By making measurements in these regions, we are able to test
current understanding of tropospheric photochemistry. Such direct
measurements often result in significant modification of our
understanding of tropospheric fate and cycling of nitrogen oxides and
other species. For example, in 1998 we discovered that NOx is
released to the atmosphere from sunlit snow in the Arctic and at
mid-latitutes. My research group and I are currently focusing on
two sets of projects aimed at assessing the impacts of anthropogenic
emissions and boreal wildfires on ozone and ozone precursors at the
hemispheric scale. We are using field measurements
at the Pico Mountain station in the Azores Islands in combination
with transport and chemical transport model (GCTM) simulations, and
novel new techniques combining the two types of models, to probe
the impacts of outflow from the United States and other source regions
on ozone and ozone precursors over the remote North Atlantic Ocean
and to assess the consistency of these measurements with GCTM
simulations. We are also conducting a series of field studies in
the Arctic and in subarctic regions, to constrain the impacts of
long-range transport of anthropogenic and biomass-burning emissions
on the composition of the arctic lower free troposphere and to
develop models of NOx release and ozone destruction in snowpacks.

International Consortium for Atmospheric Research
on Transport and Transformation (ICARTT): North America
to Europe: Overview of the 2004 summer field study,
F. C. Fehsenfeld et al., J. Geophys. Res., in review, 2006.

A study of the impact of aged boreal fire emissions
on the composition of the remote midlatitude lower free troposphere,
using measurements at the PICO-NARE station. (NSF, 2005-2008)
Despite its distance from the boreal regions, the Pico Mountain
station (in the Azores Islands in the central North Atlantic) is
frequently impacted during summer by plumes of aged emissions from
boreal fires in Alaska, Canada, and even Siberia. Because they are
made in the free troposphere, measurements at the Pico Mountain
station have proven suitable for observing impacts of the upwind
fires on ozone and ozone precursors. As a result of the long
distance of the observatory from the fires responsible, these
measurements are indicative of emissions and impacts over a large
region. In this project, we are analyzing the database of prior
Pico Mountain observations of CO, ozone, NOx, NOy and equivalent
black carbon to deduce the magnitude of large-scale fire impacts and
assess fire emissions. These analyses utilize FLEXPART transport
simulations, conducted at Michigan Tech, MOZART GCTM simulations
provided by G. Pfister at NCAR, Boreal Wildfire Emissions Model
simulations provided by E. Hyer at NRL, and a variety of satellite
products. So far, we have demonstrated that the Pico observations
imply a rather large impact of boreal fires on ozone levels over a
very large region (Lapina et al., 2006), and have deduced the
presence of a significant seasonal trend in NOx:CO emission ratios
in these fires, the result of an increase in the relative importance
of smoldering fires as the fire season progresses (Lapina et al., in
preparation).
Primary collaborations: Gabi Pfister, NCAR
(MOZART simulations of transport and transformations of emissions
from the 2004 North American boreal wildfires), Ed Hyer, NRL (Boreal
Wildfire Emissions Model-based estimation of emissions from North
American and Siberian boreal fires in 2004 and 2005.)

A study of biomass-burning and anthropogenic impacts
on arctic tropospheric chemistry using measurements at Summit,
Greenland as part of the POLARCAT International Polar Year project.
(NASA, 2007-2010)
This project will result in the first
year-round, high-altitude Arctic measurements of a suite of ozone
precursors NOx, NOy, PAN and non-methane hydrocarbons. Measurements
will be made at the GEO-Summit station at Summit, Greenland (3208 m
altitude) for a 2-year period beginning May 2008. These
measurements will be analyzed in conjunction with FLEXPART transport
modeling and simultaneous observations of CO, ozone and black
carbon, in order to identify sources and impacts of both
anthropogenic and biomass-burning emissions. This work will focus
on impacts on arctic tropospheric ozone, ozone precursors and OH
levels and will assess potential feedbacks upon snow
photochemistry.
Primary collaborators: Detlev Helmig, Univ
Colorado (NMHC measurements), A. Stohl, NILU (FLEXPART simulations),
S. Oltmans, NOAA (ozone measurements), R. Schnell, NOAA (equivalent
black carbon measurements), and G. Huey, Georgia Tech (CO
measurements).

Investigation of ozone photochemistry in lower-FT
continental outflow traveling over the North Atlantic. (NSF,
2007-2011)
This project combines new measurents at the Pico
Mountain observatory with global chemical transport model (GCTM)
simulations of North American anthropogenic pollution outflow to
assess and evaluate CTM simulations of the ultimate impact of
outflow events upon tropospheric composition. The Pico Mountain
station is uniquely capable of frequently sampling aged North
American outflow plumes traveling in the lower free troposphere.
Analyses of prior observations at the station indicate that O3
enhancements in U.S. outflow sampled there are markedly larger than
values closer to N. America and are greater than in corresponding
CTM simulations. This project will combine GEOS-Chem GCTM
simulations, high-resolution particle transport simulations using
FLEXPART and field measurements using new techniques that combine
particle transport and CTM simulations to obtain a semi-lagrangian
sampling of CTM simulations. Two seasons (late spring through early
fall) of field measurements of NO, NO2, PAN, NOy, NMHCs, CO and
ozone will be obtained, in 2008 and 2009.
Primary
collaborations: Paulo Fialho, University of the Azores, Portugal
(Pico Mountain station), Qinbin Li, NASA (GEOS-Chem simulations), Detlev
Helmig, Univ. Colorado (NMHC measurements) and Jim Roberts, NOAA
(PAN measurements).

A synthesis of existing and new observations of
air-snowpack exchanges to assess the arctic tropospheric ozone
budget. (NSF, 2007-2011)
Photochemical processes occurring within
snowpacks result in simultaneous destruction of ozone and release of
NOx and radical precursor compounds, with the result that snowpack
photochemistry can simultaneously destroy ozone (within the
snowpack) and cause the production of ozone (in the lower atmosphere
above the snowpack). In addition, biological processes in non-polar
snowpacks result in the release of NO and can destroy ozone. This
project aims to close existing gaps in understanding of snowpack
processes affecting ozone, including ozone uptake to snow and the
role of biological activity below snowpacks, NOx release from snow,
and boundary-layer ozone production resulting from snowpack
emissions of ozone precursors. A two-pronged approach including
field measurements and chemistry-climate simulations will be used.
Air/snow exchange fluxes of NOx and ozone will be determined at
three separate locations which span the range of snowpack
environments: polar glacial (at Summit, Greenland), arctic
non-glacial (at Toolik Lake, Alaska) and midlatitude (in northern
Michigan or Wisconsin). New parameterizations of snowpack processes
will be developed and incorporated into single column model versions
of the global chemistry-climate models ECHAM4 and ECHAM5-MESSy. The
expected outcome of this effort is the first assessment of the
impact of snowpack photochemical processes upon the arctic and
subarctic tropospheric ozone budget, and a modeling framework
suitable for assessing the expected impact that climate change will
exert upon the tropospheric ozone budget through changing snowcover
and permafrost extent.
Primary collaborations: Detlev
Helmig, Univ. Colorado (eddy correlation ozone flux and ozone
gradient measurements and other activities), Laurens Ganzeveld,
Univ. Wageningen, Netherlands (chemistry-climate model development
and simulations).

Chris Owen (Atmospheric transport to the central
North Atlantic region) (graduating May 2009)

Kateryna Lapina (Forest fire impacts on lower troposphere
CO and Ozone levels at the regional to hemispheric scale)
(graduating May 2009). Currently in a postdoc with
Colette Heald at Colorado State University.